1. Field of the Invention
The present invention relates to a substrate treatment method and a substrate treatment apparatus for treating a surface of a substrate such as a semiconductor substrate.
2. Description of Related Art
In a semiconductor device production process, particles are liable to adhere on a surface of a semiconductor wafer (hereinafter referred to simply as “wafer”). Therefore, it is necessary to clean the surface of the wafer in a proper step of the production process.
In an exemplary wafer surface cleaning method, droplets of a treatment liquid (cleaning liquid) are generated by mixing the treatment liquid with a gas, and caused to impinge on the wafer surface. This method is implemented by a substrate treatment apparatus which includes a bifluid nozzle adapted to generate and spout the droplets of the treatment liquid by mixing the treatment liquid with the gas. The treatment liquid droplets spouted from the bifluid nozzle are caused to impinge on the wafer, whereby the wafer is cleaned.
FIG. 14 is a schematic sectional view illustrating the construction of the bifluid nozzle provided in the conventional substrate treatment apparatus. The substrate treatment apparatus is disclosed, for example, in Japanese Unexamined Patent Publication No. 2002-270564.
The bifluid nozzle 101 includes an outer cylinder 102 serving as a casing, and an inner cylinder 103 fitted in the outer cylinder 102. The outer cylinder 102 and the inner cylinder 103 each have a generally cylindrical shape, and have a common center axis.
The inside space of the inner cylinder 103 serves as a treatment liquid channel 106, and deionized water (DIW) as the treatment liquid (cleaning liquid) is introduced into the treatment liquid channel 106 from one end of the inner cylinder 103. The treatment liquid channel 106 has an opening provided as a treatment liquid outlet port 107 at the other end of the inner cylinder 103.
In a region of the bifluid nozzle 101 axially opposite from the treatment liquid outlet port 107, the outer diameter of the inner cylinder 103 is substantially equal to the inner diameter of the outer cylinder 102, so that the inner cylinder 103 and the outer cylinder 102 are in intimate contact with each other. In an axially intermediate region of the bifluid nozzle 101 and a region of the bifluid nozzle 101 adjacent to the treatment liquid outlet port 107, the outer diameter of the inner cylinder 103 is smaller than the inner diameter of the outer cylinder 102, so that a generally annular space serving as a gas channel 104 is defined between the inner cylinder 103 and the outer cylinder 102. The gas channel 104 has an annular opening provided as a gas outlet port 108 around the treatment liquid outlet port 107. The treatment liquid outlet port 107 and the gas outlet port 108 are disposed adjacent each other.
A gas inlet pipe 105 is connected to the bifluid nozzle 101, and extends through the outer cylinder 102 with its inside space communicating with the gas channel 104. High-pressure nitrogen gas can be introduced into the gas channel 104 through the gas inlet pipe 105.
When the deionized water and the nitrogen gas are simultaneously introduced into the treatment liquid channel 106 and the gas channel 104, respectively, the deionized water and the nitrogen gas are discharged from the treatment liquid outlet port 107 and the gas outlet port 108, respectively. The deionized water and the nitrogen gas respectively flow through a portion of the treatment liquid channel 106 adjacent to the treatment liquid outlet port 107 and through a portion of the gas channel 104 adjacent to the gas outlet port 108 in parallel relation.
Since the treatment liquid outlet port 107 and the gas outlet port 108 are disposed adjacent each other, the nitrogen gas discharged from the gas outlet port 108 collides (and is mixed) with the deionized water discharged from the treatment liquid outlet port 107, whereby droplets of the deionized water are generated.
When a wafer W is disposed in properly spaced relation with the treatment liquid outlet port 107 and the gas outlet port 108, the deionized water droplets impinge on a surface of the wafer W. At this time, particles adhering on the wafer surface are physically removed by the kinetic energy of the deionized water droplets.
However, the deionized water and the nitrogen gas thus discharged widely diverge outward as departing from the treatment liquid outlet port 107 and the gas outlet port 108. Therefore, the deionized water and the nitrogen gas are not efficiently mixed, making it impossible to efficiently generate deionized water droplets having smaller diameters.
As stated in Japanese Unexamined Patent Publication No. 8-318181 (1996), contaminants on the wafer can advantageously be removed when the liquid droplets have diameters of 1 μm to 100 μm. Where the diameters of the liquid droplets are within this range, the contaminant removal efficiency is virtually constant. However, a minute interconnection pattern formed on the surface of the wafer is liable to be damaged even if liquid droplets having diameters which ensure the advantageous cleaning of the wafer are employed.
The nitrogen gas discharged from the gas outlet port 108 flows ahead while widely diverging outward and, hence, the flow speed of the nitrogen gas steeply decreases as departing from the gas outlet port 108. Accordingly, the speed of the deionized water droplets carried together with the nitrogen gas to the surface of the wafer W steeply decreases. Therefore, the deionized water droplets do not have a sufficiently great kinetic energy when impinging on the wafer W, so that the wafer cleaning efficiency is low.
Further, where the bifluid nozzle 101 provided in the conventional substrate treatment apparatus is employed, the direction of the nitrogen gas discharged from the gas outlet port 108 is unstable. Therefore, the reach range of the deionized water droplets on the wafer W being treated is also unstable, making it impossible to uniformly treat the wafer W.